The present invention relates to a coated polyester hollow molded product, a regeneration method and a surface coating solution therefor. More specifically, it relates to a coated polyester hollow molded product having a coating film which can be easily removed without exerting a bad influence on the polyester hollow molded product, a regeneration method therefor and a surface coating solution for forming the coating film.
A polyethylene naphthalene dicarboxylate-based (may be abbreviated as PEN hereinafter) hollow molded product has more excellent characteristic properties than a polyethylene terephthalate-based (may be abbreviated as PET hereinafter) hollow molded product and is expected as a hollow molded product which can be salvaged and recycled.
The cleaning of a hollow molded product is necessary for recycling and generally carried out using an aqueous solution (1 to 6%) of sodium hydroxide heated at 50 to 1000xc2x0 C.
However, when alkali cleaning is made on a PEN-based hollow molded product salvaged after use, the transparency of the hollow molded product reduces. The reduction of transparency is more marked as the number of times of salvaging and recycling increases.
Although water resistance can be provided simply by coating the surface of the PEN-based hollow molded product, it is difficult to remove the coating layer for recycling, for example, the coating layer can not be removed by cleaning with hot water.
When an ultraviolet light absorbing compound is blended with a material for the hollow molded product without forming a coating layer, such a problem as the contamination of contents by a bleed-out may arise.
Further, as the PEN-based hollow molded product has high surface hardness, its surface is easily scratched and the scratching of the surface must be suppressed for salvaging and recycling.
Meanwhile, the following publications are known for water-soluble polyesters.
JP-A 10-110027 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a method of producing a hot water-soluble polyester by esterifying or carrying out an ester exchange reaction among terephthalic acid, alkali metal sulfonate group-containing aromatic dicarboxylic acid or lower alkyl ester thereof and ethylene glycol, and melt polycondensing and solid-phase polymerizing the esterified product or the product of the ester exchange reaction. The above publication teaches that the produced hot water-soluble polyester can be used as a material for forming a pattern by dissolving a required portion with hot water after the formation of a fabric.
JP-A 8-176284 discloses a water-soluble polyester which contains an ion dissociable group-containing dicarboxylic acid component and/or an ion dissociable group-containing glycol component in the molecular main chain of the polyester in an amount of 51 mol % or more based on the total of all the acid components, is produced at a polymerization temperature of 1800xc2x0 C. or higher and lower than 2400xc2x0 C. and has an intrinsic viscosity measured in orthochlorophenol at 350xc2x0 C. of 0.25 or more. The above publication teaches that this water-soluble polyester is useful for the production of a low charged adherent polyester film which is useful for package materials, magnetic cards, magnetic tapes, magnetic disks, printing materials and the like.
It is an object of the present invention to provide a coated polyester hollow molded product which eliminates the possibility of contaminating its contents, retains excellent transparency even after it is salvaged and recycled and can be recycled with substantially no scratched surface.
It is another object of the present invention to provide a surface coating solution which is used for the production of the coated polyester hollow molded product of the present invention.
It is still another object of the present invention to provide a method of regenerating the coated polyester hollow molded product of the present invention for recycling.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a coated polyester hollow molded product comprising:
(A) a polyester hollow molded product, and
(B) a polyester coating layer formed on the exterior surface of the hollow molded product.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by a surface coating solution for a polyester hollow molded product, which contains 1 to 40 wt % of a polyester comprising 92.99 to 60 mol % of at least one dicarboxylic acid unit selected from the group consisting of naphthalene dicarboxylic acid unit and terephthalic acid unit, 0.01 to 20 mol % of an isophthalic acid unit and 7 to 20 mol % of an isophthalic acid unit having a sulfonic acid metal salt group based on the total of all the dicarboxylic acid units as dicarboxylic acid components, and 65 to 95 mol % of an ethylene glycol unit and 35 to 5 mol % of a diethylene glycol unit based on the total of all the diol units as diol units, 0.1 to 10 wt % of a surfactant and a liquid medium.
According to the present invention, thirdly, the above objects and advantages of the present invention are attained by a method of regenerating a coated polyester hollow molded product comprising the steps of preparing the salvaged coated polyester hollow molded product of the present invention, removing a polyester coating layer for the hollow molded product and forming anew polyester coating layer on the surface of the hollow molded product from which the polyester coating layer has been removed.
The present invention will be described in detail hereinbelow.
A description is first given of the coated polyester hollow molded product of the present invention. The polyester hollow molded product (A) constituting the coated polyester hollow molded product comprises preferably an aromatic polyester, more preferably an aromatic polyester which comprises a recurring unit selected from the group consisting of ethylene-2,6-naphthalene dicarboxylate unit and ethylene terephthalate unit in an amount of at least 85 mol % based on the total of all the recurring units. The aromatic polyester may be used alone or blended with two or more types of another aromatic polyester.
Polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are particularly preferred as the aromatic polyester.
The intrinsic viscosity of the aromatic polyester is preferably 0.5 to 1.0, more preferably 0.55 to 0.8, particularly preferably 0.55 to 0.75. When the intrinsic viscosity is lower than 0.5, blowing properties worsen, thereby making it difficult to obtain a molded product having a uniform thickness. When the intrinsic viscosity is higher than 1.0, elongation stress becomes high, which might be the cause of hazing a molded product.
The polyester hollow molded product made from the above polyester can be produced by employing a known general molding technique. Examples of the applicable molding method include biaxial orientation blow molding techniques (cold parison method and hot parison method), injection blow molding technique and direct blow molding technique. In addition, a molding technique in which a hollow molded product is formed after the polyester is molded into a sheet form may be used. The polyester hollow molded product may be a bottle.
Preferably, the polyester coating layer (B) formed on the exterior surface of the polyester hollow molded product has a weight reduction of 3 wt % or less when it is treated with 25xc2x0 C. water for 2 hours and is removed when it is treated with an alkali aqueous solution having a temperature of 750xc2x0 C. and a pH of 11.6 for 9 minutes.
When the weight reduction is 3 wt % or less after 2 hours of a treatment with 250xc2x0 C. water, the polyester hollow molded product is circulated in the market and used as a vessel and the coating layer is substantially retained even after it contacts water during this. When the weight reduction is larger than 3 wt %. the coating layer substantially falls off or peels off from the hollow molded product, thereby causing an appearance problem. The weight reduction is more preferably 2 wt % or less.
The coating layer can be easily removed from the polyester hollow molded product circulated and used as a vessel under alkali conditions in the cleaning step when it is treated with an alkali aqueous solution having a temperature of 75xc2x0 C. and a pH of 11.6 for 9 minutes. When the coating layer can be removed with an alkali aqueous solution under such conditions, the coating layer can be removed with hot water heated at 60 to 100xc2x0 C., preferably 70 to 95xc2x0 C. and a pH of 5.5 to 8.5, preferably 6 to 8 in most cases.
The preferred polyester coating layer (B) having the above properties is made from a polyester which comprises 92.99 to 60 mol % of at least one dicarboxylic acid unit selected from the group consisting of naphthalene dicarboxylic acid unit and terephthalic acid unit, 0.01 to 20 mol % of an isophthalic acid unit and 7 to 20 mol % of an isophthalic acid unit having a sulfonic acid metal salt group based on the total of all the dicarboxylic acid units as dicarboxylic acid components and 65 to 95 mol % of an ethylene glycol unit and 35 to 5 mol % of a diethylene glycol unit based on the total of all the diol units as diol units.
Examples of the naphthalene dicarboxylic acid unit include 2,6-naphthalene dicarboxylic acid and 2,7-naphthalene dicarboxylic acid, out of which 2,6-naphthalene dicarboxylic acid is particularly preferred.
The naphthalene dicarboxylic acid unit and the terephthalic acid unit maybe derived from an ester derivative. Examples of the ester derivative include methyl esters, ethyl esters, propyl esters and butyl esters, out of which methyl esters are preferred.
The amount of at least one unit selected from naphthalenedicarboxylid acid unit and terephthalic acid unit is 60 to 92.99 mol % based on the total of all the dicarboxylic acid components. When the amount is smaller than 60 mol %, the water resistance of the polyester lowers and when the amount is larger than 92.99 mol %, the solubility in hot water of the polyester deteriorates. Further from the viewpoint of solubility in hot water, the amount of the naphthalene dicarboxylic acid unit is preferably 50 mol % or less based on the total of all the dicarboxylic acid components.
The amount of the naphthalene dicarboxylic acid unit is preferably 0 to 50 mol %, more preferably 0 to 30 mol %, particularly preferably 0 to 10 mol % based on the total of all the dicarboxylic acid components to obtain excellent solubility in hot water.
Examples of the isophthalic acid unit include isophthalic acid and derivatives thereof such as methyl, ethyl, propyl and butyl esters.
The amount of the isophthalic acid unit is 0.01 to 20 mol %, preferably 0.01 to 15 mol %, particularly preferably 5 to 10 mol % based on the total of all the dicarboxylic acid components. When the amount is smaller than 0.01 mol %, the crystallinity of the polyester becomes too high. When the amount is larger than 20 mol %, reductions in polymerization reactivity and crystallinity become large.
Examples of the isophthalic acid unit having a sulfonic acid metal salt group include 5-lithium sulfoisophthalic acid, 5-sodium sulfoisophthalic acid and 5-potassium sulfoisophthalic acid, out of which 5-sodium sulfoisophthalic acid is particularly preferred.
They may be derived from a derivative. Examples of the derivative include esters such as methyl esters, ethyl esters, propyl esters and butyl esters, out of which methyl esters are particularly preferred.
The amount of the isophthalic acid unit having a sulfonic acid metal salt group is 7 to 20 mol %, preferably 8 to 15 mol %, particularly preferably 9 to 13 mol % based on the total of all the dicarboxylic acid components. When the amount is smaller than 7 mol %, solubility in hot water becomes insufficient and when the amount is larger than 20 mol %, reactivity at the time of polymerization deteriorates and melt viscosity becomes too high, thereby reducing productivity.
The amount of the ethylene glycol unit is 65 to 95 mol % based on the total of all the diol components.
The amount of the diethylene glycol unit is 5 to 35 mol %, preferably 10 to 35 mol %, particularly preferably 10 to 25 mol % based on the total of all the diol components. When the amount is smaller than 5 mol %, solubility in hot water lowers and when the amount is larger than 35 mol %, deterioration caused by thermal decomposition becomes large.
The diethylene glycol unit may be derived from a diethylene glycol component which is added at the time of polymerization or may be produced by a polymerization reaction.
The polyester of the polyester coating layer (B) is particularly preferably a polyester which comprises the isophthalic acid unit having a sulfonic acid metal salt group in an amount of 8 to 15 mol % based on the total of all the dicarboxylic acid units and the ethylene glycol unit in an amount of 75 to 95 mol % based on the total of all the diol units.
The polyester has an intrinsic viscosity of preferably 0.2 to 0.5, more preferably 0.25 to 0.45. When the intrinsic viscosity is lower than 0.2, chipping at the time of polymerization becomes difficult and strength becomes low disadvantageously. When the intrinsic viscosity is higher than 0.5, productivity at the time of polymerization lowers and solubility in hot water deteriorates disadvantageously.
The glass transition temperature of the polyester is preferably in the range of 55 to 90xc2x0 C.
Out of the above polyesters for the polyester coating layer (B), a polyester having the following properties (1), (2) and (3) can increase the functionality of the polyester coating layer (B) because it eliminates the possibility of contaminating the contents of the hollow molded product and can retain excellent transparency and a substantially unscratched surface even when the hollow molded product is salvaged and recycled;
(1) a solubility in water heated at 95xc2x0 C. of 10 wt % or more,
(2) a solubility in water heated at 30xc2x0 C. of 1 wt % or less, and
(3) a reduction in intrinsic viscosity after 1 hour of a treatment with water heated at 95xc2x0 C. of 0.01 at maximum.
The polyester can be produced by the following method. For example, it can be produced by esterifying or carrying out an ester exchange reaction among terephthalic acid or ester forming derivative thereof (preferably dimethyl ester), isophthalic acid or ester forming derivative thereof (preferably dimethyl ester), isophthalic acid having a sulfonic acid metal salt group or ester forming derivative thereof (preferably dimethyl ester), 2,6-naphthalene dicarboxylic acid or ester forming derivative thereof (preferably dimethyl ester) and ethylene glycol (diethilene glycol is added as the case may be) under heating.
In the case of the ester exchange reaction, a cobalt, manganese, calcium, magnesium and/or titanium compound may be used as a catalyst.
To control reactivity and the content of diethylene glycol, an alkali metal is preferably added. The alkali metal is preferably lithium, sodium or potassium. Out of these, sodium is preferred. The amount of the alkali metal is preferably 10 to 400 mmols, more preferably 100 to 250 mmols based on 100 mols of the total of all the dicarboxylic acid components.
Subsequently, a polycondensation reaction is carried out under heating and vacuum in the presence of a germanium, antimony and/or titanium catalyst(s) and a phosphorus compound.
The phosphorus compound is preferably an inorganic phosphoric acid such as phosphoric acid, hypophosphorous acid or phosphorous acid, or organic phosphoric acid such as trimethyl phosphate.
As desired, the polymer is then formed into a chip, pellet or block and ground before use.
The coating layer can be formed by applying a liquid coating solution containing this surface coating polyester to at least the exterior surface of the polyester hollow molded product and drying it.
A description is subsequently given of the surface coating solution.
The surface coating solution of the present invention contains the surface coating polyester in an amount of 1 to 40 wt %. When the amount is smaller than 1 wt %, film formation is difficult and when the amount is larger than 40 wt %, the viscosity of the solution becomes high, thereby making it difficult to handle the solution.
According to the present invention, there is provided a solution which contains 1 to 40 wt % of a specific polyester, 0.1 to 10 wt % of a surfactant and a liquid medium as a preferred surface coating solution as described above.
The surfactant may be ionic or nonionic. Preferably, it is polyethylene glycolorpolyoxyethylene sorbitan alkylate. These surfactants are preferably used in combination. That is, in a preferred aspect of the present invention, the surfactant is a mixture of polyethylene glycol and polyoxyethylene sorbitan alkylate in a weight ratio of preferably 10:1 to 1:5, more preferably 10:1 to 1:2 from the viewpoints of film forming properties at the time of coating and water resistance.
The surface coating solution of the present invention contains the surfactant in an amount of 0.1 to 10 wt %, preferably 0.1 to 5 wt %. When the surfactant is contained in the above range, wettability at the time of applying the coating solution for forming a coating layer becomes satisfactory and the removal of the formed coating layer with hot water or the removal of the coating layer with an alkali aqueous solution becomes easy. When the amount is larger than 10 wt %, solubility in normal temperature water increases.
The polyethylene glycol is preferably liquid with a low viscosity, particularly preferably liquid with a molecular weight of 200 to 1,000.
The polyoxyethylene sorbitan alkylate is preferably polyoxyethylene sorbitan oleate, polyoxyethylene sorbitan stearate or polyoxyethylene sorbitan palmitate, particularly preferably polyoxyethylene sorbitan oleate.
The surface coating solution is preferably a water solution or water dispersion prepared by dissolving or dispersing the above components in water. For dissolution or dispersion, hot water, preferably hot water heated at 60 to 100xc2x0 C. is desirably used from the viewpoints of sanitation and handling safety.
In the case of a water solution, the surface coating polyester is dissolved in hot water, preferably hot water heated at 60 to 100xc2x0 C., in preferably 20 hours or less, more preferably 10 hours or less, particularly preferably 3 hours or less. This is aimed to suppress hydrolysis. The amount of the surface coating polyester is preferably 1 to 40 wt %, more preferably 5 to 20 wt %. The amount is suitably controlled to this range by a coating method or the thickness of a coating film. When the amount of the surface coating polyester is smaller than 1 wt %, the thickness of the coating film is small and nonuniform disadvantageously. When the amount is larger than 40 wt %, the amount of the residual polyester undissolved in hot water increases, the viscosity of the solution rises, and coatability deteriorates disadvantageously.
As a dispersing means, the surface coating polyester is dissolved in an organic solvent such as ethanol, methanol, isopropyl alcohol, chloroform, acetone, methyl ethyl ketone or ethyl acetate in a high concentration and mixed with water.
In either one of the cases of a water solution and a water dispersion, the surfactant may be contained in the surface coating solution and may be added in any stage.
The surface coating solution of the present invention preferably has a haze value at 25xc2x0 C. of 30% or less, a pH of more than 5 and less than 7, a viscosity of 0.5 Pa-s or less and an electric conductivity of 100 to 4,000 xcexcS/cm.
The surface coating solution of the present invention may contain at least one agent selected from the group consisting of an ultraviolet light absorbent and colorant.
The surface coating solution of the present invention is novel as a solution for coating the surface of a polyester hollow molded product.
Therefore, according to the present invention, there is further provided use of the surface coating solution of the present invention which comprises 1 to 40 wt % of the above specific polyester, 0.1 to 10 wt % of a surfactant and a liquid medium for coating a polyester hollow molded product.
The coating layer formed by using the surface coating solution of the present invention provides the effects of preventing the exterior surface of a hollow molded product from being scratched, burying a small scratch and preventing the appearance from being marred. Further, it has the ability of absorbing ultraviolet radiation and provides the effect of suppressing the deterioration of the polyethylene naphthalene dicarboxylate of the polyester hollow molded product by ultraviolet radiation when it is used, salvaged and kept.
The haze value of the barrel portion of the polyester hollow molded product having this coating layer of the present invention is preferably 5% or less, more preferably 2% or less at a thickness of 300 xcexcm. When the haze value is larger than 5%, transparency is low and the appearance as one of the values of a commercial product is marred if the polyester hollow molded product is used as a bottle to be filled with a drink.
The thickness of the coating layer is preferably 0.1 to 10 xcexcm, more preferably 0.1 to 5 xcexcm, much more preferably 0.2 to 2 xcexcm. When the thickness is smaller than 0.1 xcexcm, an optical deterioration suppression effect obtained by coating the surface of the hollow molded product is low disadvantageously. When the thickness is larger than 10 xcexcm, the removal of the coating layer with hot water or an alkaline aqueous solution takes long disadvantageously.
The coating layer may include in an amount of 5 to 50 parts by weight based on 100 parts by weight of the polyester, derived from the surfactant contained in the coating solution.
In the present invention, this coating layer is renewed by removal and regeneration each time the polyester hollow molded product is re-used.
Therefore, according to the present invention, as described above, there is provided a method of regenerating a coated polyester hollow molded product comprising the steps of preparing the salvaged coated polyester hollow molded product of the present invention, removing a polyester coating layer from the hollow molded product, and forming a new polyester coating layer on the surface of the hollow molded product from which the polyester coating layer has been removed.
The step of removing the coating layer is preferably a step including cleaning with heated water or alkaline aqueous solution and cleaning with water thereafter.
For cleaning with heated water or alkaline aqueous solution, the temperature of the water or alkaline aqueous solution used for removing the coating layer is preferably 60 to 100xc2x0 C., more preferably 65 to 95xc2x0 C. When the temperature is lower than 600xc2x0 C., satisfactory cleaning cannot be carried out, the coating layer cannot be completely removed and a further a sterilizing effect cannot be expected disadvantageously. When the temperature is higher than 100xc2x0 C., the thermal deformation of the polyester hollow molded product is caused disadvantageously. When the alkaline aqueous solution is used, sodium hydroxide is preferably used in a concentration of 1 to 6%.
For cleaning with heated water or alkaline aqueous solution, the polyester hollow molded product is preferably immersed in the above heated water or alkaline aqueous solution. As the case may be, the heated water or aqueous solution may be sprayed onto the polyester hollow molded product.
For cleaning with water after cleaning with heated water or alkaline aqueous solution, water heated at 95xc2x0 C. or less is preferably used. This cleaning may be carried out to such an extent that the alkaline aqueous solution is washed away completely.
In the present invention, the coating layer is renewed by forming a new coating layer on the polyester hollow molded product from which the coating layer has been removed so as to regenerate the polyester hollow molded product. The method of forming this coating layer may be the method of forming a coating layer when a polyester hollow molded product is to be produced. To this end, the surface coating solution of the present invention is preferably used.
The renewal of the coating layer is preferably carried out each time the polyester hollow molded product is re-used. That is, each time it is re-used, it is preferably used to apply such a method that the polyester hollow molded product is regenerated by the above regeneration method.
The polyester hollow molded product can be used repeatedly by renewing the coating layer by this regeneration method and the haze of a barrel portion having a thickness of 300 xcexcm when the polyester hollow molded product is used 20 times repeatedly can be adjusted to 5% or less, preferably 2% or less. When it is used repeatedly, the polyester hollow molded product is exposed to the ultraviolet radiation of the sunlight and the exposed dose of ultraviolet radiation having a wavelength range of 310 to 400 nm is estimated at 7,500 mJ/cm2 to 90,000 mJ/cm2 for one time of use.